Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

348
FXUS63 KLOT 242355
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
655 PM CDT Tue Mar 24 2026

.KEY MESSAGES...

- Warm and dry conditions and breezy winds will lead to an
  elevated danger for grass/brush fire ignition and spread
  tomorrow.

- A warming trend will continue through Thursday, when high
  temperatures are forecasted to peak in the 70s and 80s.

- Showers and thunderstorms are likely to develop near and just
  behind a cold front Thursday afternoon and evening. There is a
  level 2/5 threat for severe thunderstorms south of I-80.

- Dramatically colder temperatures are expected behind the cold
  front late Thursday through Friday.

&&

.DISCUSSION...
Issued at 313 PM CDT Tue Mar 24 2026

Modest southerly return flow has allowed for temperatures to
creep toward and into the 50s this afternoon in spite of an
expansive and opaque mid- to upper-level cloud canopy streaming
overhead. After a milder (though still seasonably cool) night,
our warming trend will continue tomorrow with temperatures
peaking in the upper 60s to low-mid 70s amidst thinner and less
opaque upper-level cloud cover and breezier south-southwesterly
winds. Dew points also look like they`ll be on a general upward
trend through tomorrow, though should still maintain enough
separation from air temperatures for minimum relative humidity
values of around 20-25% to be observed -- primarily across the
southeastern half of our forecast area (minimum RH values closer
to 30-35% are more likely across our northwest). In addition,
10-hour fuel moisture values also look like they`ll be butting
up against Red Flag Warning criteria tomorrow afternoon.
However, while it`ll be breezy, our sustained 20-foot winds
likely won`t quite reach their respective Red Flag Warning
threshold, so we`ll just stick with messaging tomorrow as an
elevated fire danger day.

Tomorrow night, warm air advection/isentropic ascent will ramp
up over the region as a low-level jet strengthens. Mid-level
lapse rates will also steepen as a mid-level shortwave trough
drifts through the area, priming thermodynamic profiles to be
supportive for elevated convection. Whether this elevated
convection will ultimately materialize will be contingent upon
sufficient low-level saturation being realized at the base of
the elevated mixed layer, and considerable spread remains in
model guidance as to whether this will happen in our CWA, to the
east of us, or even at all. Thus, have kept PoPs capped in the
low-end chance range and focused across our southern CWA, where
there will be more time for sufficient low-level saturation to
occur as the southwest-northeast oriented low-level jet slides
across our area from west to east. If everything comes together
just right, then the strongest cells that develop tomorrow night
would be capable of producing lightning and small hail (though
some isolated instances of 1+" diameter hail could not be
completely ruled out in the worst case).

With warm/moist advection essentially continuing uninterrupted
through this time, Thursday is shaping up to be a downright
summer-like day for at least southern portions of our forecast
area, where temperatures are forecasted to climb into the low-
mid 80s while dew points potentially rise into the 60s. Farther
north, a greater degree of cloud cover and an earlier arrival
time of a powerhouse cold front should prevent temperatures
from climbing as high as they will farther south, though it will
still feel unseasonably warm with temperatures largely in the
70s prior to the arrival of the cold front. Chicago`s record
high temperature for March 26th (79F set back in 2007) could
very well at least be threatened, though Rockford`s daily high
temperature for this date (81F, set back in 1907) looks like it
will probably remain safe.

The unseasonably warm and moist conditions ahead of the
incoming front will set the stage another round of potential
severe thunderstorms Thursday afternoon and evening as the front
plows through the region. Initially, a pronounced capping
inversion will stave off any attempts at convective initiation
through the early afternoon. However, the available model
guidance at this time range remains in fairly good agreement
that the cap will slowly be chipped away at over the course of
the day via diurnal heating and warm air advection before strong
lift induced by the front and augmented by a mid-level
disturbance zipping in from the west finishes off the remaining
convective inhibition by sunset, with robust convection ensuing
near the front thereafter. Thus, how quickly the cold front
progresses southward will be instrumental in dictating which
parts of our area will have a threat for severe thunderstorms
late in the day on Thursday, with only anafrontal showers
expected to occur well north of the front. The latest Day 3
Convective Outlook from the Storm Prediction Center looks
reasonable at this time, with locations south of I-80 (and more
so near/south of the Kankakee River) at greater risk for severe
weather compared to areas farther north.

Key questions that remain at this time for this potential
severe weather event revolve around storm mode and whether
storms will be surface-based at all or whether they`ll be
predominantly elevated/post-frontal. The progged strong to
extreme effective bulk shear would be supportive of the
development of supercells (at least initially), though the
strong lift and a deep-layer shear vector orientation that may
end up being parallel to the front could result in relatively
quick upscale growth into an MCS. Any mature and at least semi-
discrete supercellular structures would likely feature large to
potentially very large (2+" in diameter) hail as their primary
hazard given the magnitude of the shear and the presence of
long, relatively straight hodographs, while the damaging wind
threat would be greater if/once a consolidated MCS develops. If
any storms were to develop and remain along/ahead of the front,
then some tornado threat could materialize too. However, unlike
on March 10th, this front will likely just keep hauling
southward without a stronger surface low nearby to stall its
forward progress, and thus, any storms that develop near/along
it are more likely to get undercut and quickly become elevated
than they are to remain surface-based for a sustained period of
time. Trends in forecast guidance and the strength/depth of the
cold front will closely need to be monitored, though.

Thursday`s cold front is likely to become lake-enhanced and
send temperatures crashing 20-30+ degrees behind it over a
short period of time. With northerly winds persisting through
Friday, it will remain decidedly colder with daytime highs only
forecasted to be in the mid 30s to mid 40s, coldest near and
immediately downwind of Lake Michigan. Temperatures should,
however, start to moderate over the weekend with no
precipitation expected through this time.

Ogorek

&&

.AVIATION /00Z TAFS THROUGH 06Z THURSDAY/...
Issued at 655 PM CDT Tue Mar 24 2026

Forecast concerns for the terminals...

- Breezy southwest winds on Wednesday gusting 20-25 kts.

- Low chance (10-15%) for scattered showers and isolated storms
  Wednesday night.


A surface high continues to traverse across the eastern Great
Lakes which is maintaining SCT to BKN VFR skies over northern IL
and northwest IN. These skies are expected to persist through
the TAF period with otherwise mostly dry conditions. Winds will
continue to turn southeasterly this evening as the high departs
with speeds around 5-10 kts. Directions will become more
southerly towards daybreak before settling into a southwest
orientation by Wednesday afternoon. Speeds will also be
increasing on Wednesday with 20-25 kt gusts expected for the
afternoon hours. While gusts should diminish Wednesday evening,
increasing warm advection may allow the atmosphere to remain
mixed so cannot completely rule out some occasional 20+ kt gusts
Wednesday night.

There is also a low chance (10-15%) for a couple of scattered
showers and/or isolated thunderstorms late Wednesday evening
and night as a subtle disturbance pivots across northeast IL.
Forecast soundings during this period do show decent instability
present, but the more limited moisture makes the coverage of
any showers/storms at the terminals very low confidence at this
point. Thus, have maintained a dry forecast but will be keeping
a close eye on trends going forward.

Yack

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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